Due to more stringent applications there is a need for pressure transducers capable of operating at high temperature, while further being of small physical dimensions to enable use of the same in small areas.
Such uses exist in many areas, such as satellite applications, nuclear power, chemical processing, aerodyromics, engine testing and so on.
The semiconductor piezoresistive transducers are in widespread application due to the high output signals available.
The high signal output is desirable, and coupled with this is the fact that when one wishes to provide small transducers (less than 1/8 inch in diameter) the use of semiconductor technology is essential.
The prior art is replete with various techniques for fabricating such transducers.
Certain techniques use organic epoxy adhesives to bond several sensors to a central, metal diaphragm. The metal diaphragm deflects under force and the transducers bonded thereon sense the surface strains on the diaphragm. Difficulties at high temperature operation are paramount due to the "plastic" behavior of the epoxy; and sensors which use epoxy exhibit hysterisis and zero instability. Both terms indicating that such a transducer would exhibit varying quiescent condition operation due to such temperature changes.
With the introduction of monolithic devices, sensors were fabricated integrally with a silicon diaphragm. The integral configuration permitted higher temperature operation; but at temperatures of about 350.degree.F the isolation between the sensors and the substrate deteriorated. This was caused by thermally generated carriers which served to short circuit the sensors to the substrate.
It is therefore an object of this invention to provide improved pressure transducers and techniques for fabricating the same capable of operating at high temperatures. Such transducers being capable of operating at temperatures above 600.degree.F.
A preferred embodiment of the invention comprises a pressure transducer comprising a silicon disc-like diaphragm having located on a first surface thereof at least one dielectric insulating member, said insulating member having a piezoresistive sensor element on a surface thereof to thereby form a composite transducer structure wherein said sensor is dielectrically isolated from said diaphragm, an annular ring housing generally cylindrical in shape having an open top end of a diameter less than the diameter of said disc and a glass bond coupling said disc to said housing, located about the periphery of said disc, with the area defined by said open top end of said housing surrounding said sensor.
Further embodiments include methods of securing pressure transducing assemblies to housing for high temperature operation.